Polishing metals and composition therefor



Uni cdwstatc -Pousnns N GMETALS ANn.. coMrosrm John 6. Beach to Untted States of Anierica as represenfed by the United States Atomic Energy Commission No Drawing. Application December 31, 1953, Serial No. 401,742

4 Claims. (Cl. 4l42) satisfactory because the reaction was too violent and too difficult to control. A mixture of hydrofluoric acid andammonium fluoride has also been employed and this mixture has given very satisfactory results. This method using hydrofluoric acid and ammonium fluoride forms the subject matter of copending application, Serial No. 355,858, filed by John G. Beach et al. on May lS,f 1953. However, in some instances, for instance when zirconium contains occlusions of zirconium carbide, a smooth surface cannot be obtained with a solution of ammonium bifluoride or a mixture of ammonium fluoride and hydrofluoric acid; the surface then shows a relief pattern formed by zirconium carbide granules. 1

A mixture of hydrofluoride acid, ammonium fluoride and nitric acid was also examined for polishing Group VI- metals. A mixture containing 60 grams of ammonium bifluoride per liter in a 50% (byvolume) nitric acid (70%) was used for polishing zirconium containing some tonly .en ploy dglt -isz finally also antob ecttoisthisdnvention toprovide '0 a. method: and E asolntion for polishing; Group -'IV-.me'tals may .be. satisfaef wherebyiternperature as. lawns; 602B are"accomplishedhylimmersing the article to be polished in anaqueous solution containing a water-soluble fluoride, nitric acid and fluosilicic acid. The optional operating temperature is'about .60 F.; how-.

ever, it may vary-.widely. 7

While no treatment is necessary. prior to immersion into the polishing'solution, it has been found advantageous to remove any scale adheringto thesurface by sandor vapor-blasting. I

' I The concentrations of the various components of the polishing solution may vary widely. However, ranges of from 350 to 600 cc.of nitric acid (70%,), 175 to' 400 cc.of fluosilicic acid and at least grams of:

a water-soluble fluoride, such as hydrogen fluoride, am-

monium bifluoride or ammonium fluoride, all per 1 liter I i of solution have been found preferable. Th'efcontent of ammonium fluoride or bifluoride may reach saturation; The best results were obtained with-a solutioncontainin'g 400 cc. of nitric acid, 200 cc. of 30% fluosilicic f acid andSO to l00grams of ammoniumfluorideper liter of solution.

In the following example one embodimentof the in-- it vention is. given in detail.

' 1 Example w g I p Zirconium metal was'immersed .in a solution containing '100 grams of ammonium bifluoride, 400 cc. of a 70% nitric acid and 200 cc. of a 30% fluosilicic acid pe'rll liter zirconium carbide; it was found that both the zirconium exothermic and the temperature is liable togo above 130 F. and the mixture is very unstable at temperatures above 140 F. and starts to decompose. lIt is very difof solution. Immersion 'was carried out at variousf-tem-,

peratures and the thicltnesses of zirconium removed thereby in each instance from each surface per minute were measured. The results are summarized below.

v I removed/mim/surface' 70 to F 0.0006" so" was F 0.000s" to 'F.... 0.001s" to F 0.002s" 110 to F 0.o,o4"

' All surfaces of the zirconium after the treatments at the various temperatures weres'mooth, bright and-uniform.:

Similar results were obtained byftreating titanium, tin and lead witha solution identically composed.

Satisfactory results were obtained with Group IV-' metalsusing solutions containing 480 cc. of 70% nitric i acid, 320cc. of a 30% fluosilicic acid and l9SJcc. of a"- 50% hydrofluoric acid, on solution containing 600 cc.

of a 70% nitric acid, 400cciof a 30% fluosilicic acid and saturated in ammonium fluoride or ammonium bifluoride,

ficult to control the operating temperature within a range as narrow as that from to F. Another disadvantage frequently encountered with the bifluoridemitric acid mixture is the formation of noxious fumes at these high temperatures.

It is an object of this invention to provide a method and a solution for polishing Group IV-metals by which the above-described disadvantages are overcome. I It is another object of this invention to provide a method and a solution for polishing Group IV-metals' whereby the metals are made suitable for plating, and in particular for electroplating, so that the coating obtained thereby is bonded firmly to the polished article. 7 It is another object of this invention-to provide a method and a solution for polishing Group IV-metals whereby the reaction can be controlled easily.

It is still another object of this invention to provide a method and a solution for polishing Group IV-metals whereby no noxious fumes are developed.

metal containing zirconium. carbide occlusions compris-' zirconium prior to or a solution containing 356 ccof a 70% nitricacid, 178 cc. of a 30% fluosilicic acid and 109 cc. of a 50% hydrdfluoricacid. 1

The invention'is applicablefor .all' purposes where a smooth surface is desired, and in particular for electroplatingQas has been mentioned before. For instance, the.

invention is suitable par excellence as a p'retreatment'of electroplating witha metal, e. g. with nickel. V v V It will be understood that this invention is not to be limited tothe details givenherein but that it may be" modified within the scope of the appended claims. What is claimed is: 1. A process of polishing the surface of zirconium ing immersing said surface into' anv aqueous solution of about 60.to 85 F. consisting, per one liter of solution, I.

of water, at least 50 grams of a water-soluble fluoride,

350 to 600 cc. of concentrated nitric acid and from i to 400 cc. of a 30% fluosilicic acid.

2. The process'ofclaim 1 in which the solution cum from 50 to 100 grams of ammonium bifluoride, 400 cc. tains from 50 to-l00 grams of ammonium bifiuoride, of a-70% nitric acid,-and 200 cc. of 21-30% fluosilicic 400 cc. of a 70% nitric acid, and 200 cc. of a 30% fiuoacid. silicic acid per one literof solution.

'3. An aqueous solution for chemically polishing the 5 References 111 file of ihls P surfaces of zirconiumcontaining zirconium carbide occlu- UNITED STA ES P S sio ns consisting; per one'liter of solution, of 175. to 400 1: z r I cc. of a 30% fiuosilicic acid, 350 to 600 cc.-of a 70% $323235??? g1 nitric acid, and at least 50 grams of water-soluble fluorldc. 7, 2,678,811 5 spopngrH H May 18, 71.954

4. The solution of claim 3 in which the contents are 10 

1. A PROCESS OF POLISHING THE SURFACE OF ZIRCONIUM METAL CONTAINING ZIRCONIUM CARBIDE OCCLUSIONS COMPRISING IMMERSING SAID SURFACE INTO AN AQUEOUS SOLUTION OF ABOUT 60 TO 85*F. CONSISTING PER ONE LITER OF SOLUTION OF WATER, AT LEAST 50 GRAMS OF THE WATER-SOLUBLE FLUORIDE 350 TO 600 CC OF CONCENTRATED NITRIC AND FROM 175 TO 400 CC. OF A 30% FLUOSILIC ACID. 